Method and apparatus for an automatic load balancing and back-up of a multi-users network

ABSTRACT

The invention aims to implement the Load Balancing/Backup function in a Multi-Users environment and to allow a remote station to have an alternate route through another Token Ring DLC to backup. By directing the connection to another route, it postpones the connection from a remote station to a Token Ring user through a first selected Token Ring DLC for a predetermined delay. For that purpose, each Token Ring DLC stores parameters of the remote station that has an unsuccessful connection in its own Connection Cache Table. In this way, when a Test frame is received in each DLC, this latter checks in the Connection Cache Table before responding to the Test frame. The Test frame is ignored and no Test response is sent back to the remote station when the remote station is identified in the table so as to allow the remote station to detect an alternate route with a backup DLC if it exists. Each Token Ring DLC manages its own Connection Cache table which contains an entry, a source MAC address and a Source SAP and a counter indicating the number of unsuccessful attempted Test frames received from that remote station. If the counter reaches a value N, then the entry corresponding to the remote station is removed from the table. Thus, the next time a Test frame is received from this remote station, it is accepted and a response is sent from the DLC. It gives a new opportunity to the remote station to establish a connection to the user in case this latter would become available again.

FIELD OF THE INVENTION

The present invention relates to data processing in a multi-userscommunication network and more particularly to a Token Ring AutomaticLoad Balancing/Backup function in a multiple users environment.

BACKGROUND ART

The invention refers to Fe following terminology:

802.2 TEST frame: is an 802.2 Data Link Control (DLC) frame which isused for discovering a route toward a remote station.

XID frame: is an 802.2 DLC frame which is used for exchangingidentification before establishing a connection.

SABME (Set Asynchronous Balanced Mode Extended) Frame: is an 802.2 DLCframe which is used for establishing a connection.

UA (Unnumbered Acknowledgment) Frame: is an 8022 DLC frame which is usedfor confirming a connection establishment.

Routing Information: is an 802.5 MAC Frame field containing the routewhich is used for a connection (list of ring numbers and bridgenumbers).

Token Ring User: is the host computer that is shared and connected to aplurality of Token Ring stations.

MAC address: is the station address on the Token Ring.

Load Balancing function: enables to switch to another route when a routeis overloaded.

Backup function: enables to back up a route which has becomeinoperative.

Resolve Procedure: enables to discover the route to the destinationstation by means of the Test frame.

SAP: Service Access Point used for identifying a user of the DLC 802.2.All Route Broadcast implement& the broadcast function that is used forcopying the Test frame on all the rings.

The Automatic Load Balancing/Backup function is an improvement of theToken Ring Architecture. It allows an automatic balancing of the trafficbetween different Token Ring Adapters using the same MAC address, andalso automatic backup in case one of the Token Ring adapter becomesunavailable.

The U.S. Pat. No. 5,493,689 describes a system for configuring an eventdriven interface including control blocks defining good loop locationsin a memory which represent detection of a characteristic pattern. Thistechnique is a combination of a source of control vectors which sendscontrol vectors in a programmable performance vector generator which iscoupled to a data communications network to be monitored and controlled.This invention enables real-time load distribution, load balancing,problem determination, routing and customer services, but it is to beimplemented in environment that uses an expert system which analyzes theevent vectors and provides monitoring information and control signals tothe network.

The U.S. Pat. No. 5,606,693 and 5,668,986 which respectively relate to“A distributed database management over a network” and to “A method andapparatus for handling data storage requests in a distributed data baseenvironment” are dedicated to a distributed database application forlogging large volumes of data to a plurality of databases servers. Acentral configuration management is employed to balance the databaseload to direct requesting workstations to the appropriate database.Furthermore, this technique is to be implemented using workstations anddatabase servers and configuration controllers connected to a dualnetwork. In such an environment, a central configuration management anda dual network are unavoidable constraints.

FIG. 1 shows the different elements which are present in the AutomaticLoad Balancing/Backup Function.

The Token Ring User (100) activates 2 different Token Ring Data LinkControl (DLC) (102 and 112) and 2 Token Ring Adapters (103 and 113),using the same MAC address, provided the Token Ring Adapters areconnected to 2 separate rings (104 and 114).

When a remote Token Ring station (130) is to be connected to the TokenRing User (100), it uses the MAC address as its destination MAC address,and executes a Resolve Procedure to discover the route to theDestination. It first issues an All Route Broadcast Test frame assignedto the MAC address A.

Since the Test frame is sent in All Route Broadcast Mode, it is copiedon Token Ring (104) by the bridge (105) and also on the Token Ring (114)by the bridge (115). As a consequence, both Token Ring adapters (103 and113) receive a copy of the Test frame, and both respond. The RemoteToken Ring Station (130) selects the first response and establishes theconnection. This connection may be deselected in case it is overloadedor inoperative. Should the occasion arises, the second connection isestablished.

If the link between the Token Ring user (100) and one of the Token RingDLCs (for example 102) gets overloaded, this Token Ring DLC (102) doesnot respond to the Resolve procedure and the connection is establishedvia the other Token Ring DLC (112). This insures an automatic loadbalancing between the 2 Token Ring DLCs (102 and 112).

If the link between the Token Ring User (100) and one of the Token RingDLCs (for example 102) gets inoperative, this latter (102) does nolonger respond to the Resolve procedure, and the connection isestablished with the other DLC (112). This insures an automatic backupbetween the 2 Token Ring DLCs (102 and 112).

FIG. 2 shows the Normal Flow of Mono User Load Balancing.

The Remote Station (130) tries to connect to the Token Ring user (100).It first issues an All Route Broadcast Test frame assigned to the MACaddress A and SAP 0. The Test frame is then received by DLC No 1 (102)and DLC No 2 (112).

When the DLC No 1 (102) receives the Test frame command, it checkswhether a Token Ring user (100) is connected to the Token Ring Adapter(103). In such case, the DLC No 1 generates a response to the Testframe. This response contains the Routing Info field of route 1 thatconnects the Token Ring station (130) to the Token Ring user (100)through the Token Rings (120, 104, 102).

Conversely, when the DLC No 2 (112) receives the Test frame command, italso checks whether a Token Ring user (100) is connected to the TokenRing Adapter (113). Which is the case in this example. Thus, the TokenRing No 2 (112) responds to the Test frame and includes in its responsethe Routing Info field of route 2 that connects the Token Ring station(130) to the Token Ring user (100) through the Token Rings(120,114,112).

In our example, the Test response from DLC No 1 (102) is received first.The Remote Station (130) accepts the first Test frame response itreceives, indicating the shortest path, and stores the correspondingroute. This route will then be used for the transmission and receptionof all frames for this connection between the remote station (130) andthe Token Ring user (100).

In consequence, the Remote Station (130) ignores any additional Testframe response that would be received later on for this connection. TheTest frame response from DLC No 2 (112) is ignored since it is receivedafter the one from DLC No 1 (102).

Once the resolve procedure is completed, i.e. the Test frames areexchanged, the Remote Station (130) sends an XID frame to the DLC No 1(102). The XID frame which contains the routing information of Route 1,is transmitted to the Token Ring user (100).

If DLC No 1 (102) receives an XID frame assigned to Token Ring user(100), it checks if this latter is active so as to report it the XIDdata. If the Token Ring user (100) accepts the connection, DLC No 1(102) sends back an XID response to the Remote Station (130). Thislatter sends a SABME command to establish the connection with DLC No 1(102) which responds with a UA response. The connection for the route 1is then established and the data traffic can begin on this connection.

FIG. 3 describes the Normal flow of a single User Backup.

In this example, the Token Ring user (100) is not available on DLC No 1(102) but it is still available on DLC No 2 (112).

The remote station (130) sends a Test frame in the All Route Broadcastmode assigned to MAC Address A. The Test frame is then received by DLCNo 1 (102) and DLC No 2 (112).

When DLC No 1 (102) receives the Test frame, it checks if the Token Ringuser (100) is available. Since this latter is not available for DLC No1, it does not respond to the Test frame.

On the contrary, when DLC No 2 (112) receives the Test frame, it checksif the application is available for DLC No 2 so as to send back a Testframe response containing the routing information of Route 2.

The Remote station (130) receives the Test frame response from DLC No 2(112), and accepts it since it is received first. The routinginformation of Route 2 is stored and Route 2 will be used for theconnection between the remote station (130) and the Token Ring user(100).

The remote station (130) sends an XID command to DLC No 2 (112), usingthis route 2. When DLC No 2 receives the XID command, it reports the XIDdata to the Token Ring user (100) which accepts the connection. DLC No 2sends an XID response frame back to the Remote Station (130) on thisroute 2.

The remote station (130) sends a Set Asynchronous Balanced Mode Extendedcommand (SABME) to Token Ring DLC No 2 (112), which responds with anunnumbered acknowledgment response (UA). The connection is nowestablished between the remote station and the Token Ring DLC No 2. Fromnow on data traffic flows on that connection.

Statement of Problem and Solution

FIG. 4 describes the Multi User configuration which environment isalmost the same as in FIG. 1, except that a Token Ring User No 2 (400)has been added.

Both users No 1 and No 2 (410 and 400) share both Token Ring DLC No 1and No 2 (402 and 412) which are respectively connected to Token RingAdapters (403) and (413). A Remote Station (430) is connected to eachToken Ring User via 2 different routes. Route 1 is composed of TokenRing (420), Bridge (405) and Token Ring (404). Route 2 is composed ofToken Ring (420), Bridge (415) and Token Ring (414). The numeral 431indicates the path between DCL No 1 (402) is not available.

FIG. 5 describes the Flow of Multi User Load Balancing/Backup withoutthe implementation of the present invention. Remote station (430) triesto connect to Token Ring User 1 (410) which is not available for TokenRing DLC No 1 (402).

Remote station (430) sends a Test frame command in the All RouteBroadcast mode, assigned to MAC Address A The Test frame is received byboth Token Ring DLC No 1 (402) and No 2 (412).

Token Ring DLC No 1 (402) receives the Test frame command, said Testframe being assigned to SAP 0, which means there is no indication ofdestination user in Test frame. Since DLC No 1 has at least one TokenRing user (400) available (user No 2), DLC No 1 accepts the Test frameand sends back a Test frame response containing the Routing Informationof route 1. The Remote station (430) receives this Test frame responseas a first Test response for this connection. It accepts the Test frameresponse and stores this route 1.

When DLC No 2 (412) receives the Test frame command, it accepts the Testframe and sends back a Test frame response, containing the RoutingInformation of route 2.

The Remote Station (430) receives this second Test frame response. Sinceit has already received a Test frame response for this connection, theremote station ignores this additional test frame response.

The remote station (430) sends an XID to be transmitted to Token Ringuser 1 (410) by using route 1 obtained from the first received Testframe response. DLC No 1 (402) receives the XID and it checks for whichToken Ring user the XID is assigned owing to the SAP in the XID frame.DLC No 1 ignores the XID for Token Ring user 1, because this latter isunavailable.

The remote station (430) times out and retries sending XID frame forToken Ring user 1 (410) through DLC No 1 (402) which ignores them sinceToken Ring user 1 is not available on route 1.

After many failed attempts, the remote station (430) starts again with anew Test frame command. Since route 1 is shorter or has a betterresponse time than route 2, DLC No 1 (402) is always the first torespond to the Test frame. Therefore, route 1 will always be selectedand the connection between the remote station (430) and the Token Routeuser 1 (410) through the DLC No 1 (402) will always fail.

The problem is that the Test frame command contains a field SAP which isunfilled. Thus, the final destination cannot be determined at this stageand it is not possible to determine for which Token Ring user of theconnection is available. On the contrary, XID frame contains theinformation of the final destination, i.e. which Token Ring user, but atthat time, it is too late for DLC No 1. The reason of the problem isthat the Token Ring DLC cannot determine from the Test frame theidentification of the Token Ring user of the connection.

Besides, the DLC No 1 (402) is too fast to respond to the Test frame ofthe remote station (430) without taking into account the fact that TokenRing user No 1 (410) is unavailable through DLC No 1 (402). WhereasToken Ring User No 1 is available through DLC No 2 (412), but thislatter does not respond to the Test frame earlier than DLC No 1.

The limitation of the Load Balancing/Backup function in Multi Userenvironment is due to the fact that the resolve procedure Is directed toall Token Ring DLCs and not to a specific Token Ring DLC which isconnected to an available Token Ring user.

Because of this multi-user environment, the link between one of the 2Token Ring users and one Token Ring DLC may be overloaded while otherlinks are not. In such case, the Token Ring DLC still responds to theresolve procedure since one of its links is not overloaded, and theautomatic backup will fail. But if the Token Ring DLC were to ignore theResolve Procedure because one of the links is overloaded, traffic to theToken Ring user No 1 and No 2 will be backed-up on me other Token RingDLC. Such situation will interrupt all the connections if the linkbetween Token Ring DLC 2 and user 2 were to be overloaded orinoperative.

OBJECT OF THE INVENTION

The object of the invention is to suppress this limitation of the LoadBalancing/Backup function in a Multi-Users environment, by allowing aremote station to search for an alternate route through another TokenRing DLC to backup as soon as Token Ring user is unavailable through apreviously selected Token Ring DLC.

It is another object of the invention to delay the connection from aremote station to a Token Ring user through a first selected Token RingDLC for a predetermined delay.

The implementation of the automatic Load Balancing/Backup function alsocorresponds to the need in redundancy, backup and load balancing intheir single protocol network.

Furthermore, the network evolution now leads to heterogeneous networkswith different protocols, such as SNA (System Network Architecture),APPN (Advanced Peer to Peer Networking) or IP (Internet Protocol). It istherefore required to run these different protocols on the same adaptersthat are shared by a plurality of networks.

In addition, according to the present solution, it is possible to usethe Token Ring Adapters for different network protocols and to implementthe Load Balancing/Backup function.

SUMMARY OF THE INVENTION

According to the parent invention, the DLC memorizes the source MACaddress and source SAP of the N remote stations for which an XIDconnection has been refused because of an unavailable Token Ring user.These MAC addresses and SAPs are stored in a Connection Cache Table.Each Token Ring DLC has its own Connection Cache Table.

When a Test frame is received, the Token Ring DLC checks in theConnection Cache Table before responding to the Test frame. If the Testframe has been sent from a remote station whose identification isalready in the Connection Cache Table, it means this remote station haspreviously attempted to conned to an unavailable Token Ring User. Insuch case, the Test frame is ignored and no Test response is sent backto the remote station. This will allow the remote station to have achance to detect an alternate route with a backup Token Ring DLC if itexists. Otherwise, the connection attempts will be directed to the sameToken Ring DLC.

Each Token Ring DLC manages its own Connection Cache table contents.Each connection cache table entry contains, in addition to the sourceMAC address and the

Source SAP, a counter indicating the number of unsuccessful attemptedTest frames received from that remote station. When a Test frame isreceived and the source MAC address/Source SAP of that Test frame isfound in the station cache table, the Test frame is ignored but thecounter is incremented for that entry. If the counter reaches apredetermined value N, then the entry corresponding to the remotestation is removed from the connection cache table. This means that thenext time a Test frame is received from this remote station, it will beaccepted and a response will be sent from the Token Ring DLC. It willgive a new opportunity to the remote station to try to establish aconnection to the Token Ring user in case this latter would becomeavailable again.

Thus, the method of load balancing and backing up a connection incommunication network according to the present invention comprises thesteps as are set in claim 1.

The apparatus in which the method of the present invention isimplemented comprises the features that are set in claim 7.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 describes the Automatic Load Balancing and Duplicate TIC addressin a single user environment in the prior art.

FIG. 2 scribes the Normal Flow of a single User Load Balancing in theprior art.

FIG. 3 describes the Normal flow of a single User Backup in the priorart.

FIG. 4 describes the Multi User configuration and problems associatedwith it.

FIG. 5 describes the Flow of Multi User Load Backup.

FIG. 6 describes the Flow of Multi-User Load Backup according to thepresent invention.

FIG. 7 describes the XID processing in a Token Ring DLC according to thepresent invention.

FIG. 8 describes the Test frame processing according to the presentinvention.

FIG. 9 describes the Connection Cache Table format according to thepresent invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

This solution is applicable in the environment of Token Ring networksrunning multiple protocols, but could be extended to other 802.2 DLCsuch as bridged Frame Relay or ATM LAN Emulation etc

Referring again to FIG. 4, the Token Ring user No 2 (400) and Token Ringuser No 1 (410) are connected by Network Interface Card (NIC) 401 andNIC 411, respectively. The NICs are substantially identical. Therefore,the description of one is intended to cover the description of all. Afunctional representation of the NICs is shown in FIG. 4. The NIC isbased on the IEEE-802 Committee implementation of the Open SystemsInterconnection (OSI) module adopted by the International StandardOrganization (ISO). The NIC includes the adaptor (403,413) which occupythe physical layer of the OSI model. The adapter includes all thenecessary hardware and software to perform the functions described inthe standards which are incorporated herein by reference. The hardwareis well known in the art and further description is not warranted.Suffice it to say that the adapter may implement the Token Ring (802.5),ethernet (802.3), etc. In addition, the hardware may include connectors,conductive couplings, etc. the adapter includes a physical layer anddevices for coupling to the network and to the Medium Access Control(MAC) layer functions coacting operatively with a Medium AccessController to practice a desired network protocol. The Data Link Control(DLC) layer adjoins the adapter (physical layer). The (DLC) layerincludes the Medium Access Control (MAC) layer and Logical Link Control(LLC) layer. The respective layers include the functions which arenecessary to transport or route frames. The DLC further includes amemory storing information identifying remote stations and frequencywith which a remote station is unable to connect with a selectedresource in the network. A more detailed description of the respectivelayers and related hardware is set forth in the article entitled “LANIC's Let You Build Networks for PC's” by Danny Corrnier, EDN, Dec. 11,1986, (Page 136) and the IEEE related standards all of which areincorporated herein by reference.

FIG. 6 describes the Flow of a Multi User Load Backup according to thepresent invention. This scenario differs from the previous one in thatToken Ring DLC No 1 (402) keeps track of the connection failure in aConnection Cache Table.

When Token Ring DLC No 1 (402) receives an XID frame for Token Ring user1 (410) which is not available for the Token Ring DLC No 1. This latterignores the XID frame, but it stores the parameters of remote station inthe Connection Cache Table. The parameters are the Remote MAC addressand Remote SAP. Therefore, the next time a Test frame is received fromthis remote station, Token Ring DLC No 1 (402) finds its parameters inthe Connection Cache Table and ignores the Test frame command.

Token Ring DLC No 2 (412) receives the Test frame command and sends aTest frame response containing the routing information of route 2 whichconnects the remote station to the Token Ring user 1 (410) through theToken Rings (420,414) and the Token Ring DLC No 2 (412). Since theremote station receives this Test frame response first, it stores thisroute 2. Furthermore, it sends an XID frame to Token Ring user 1 (410)by using this route 2.

Token Ring DLC No 2 (412) receives the XID frame assigned to Token Ringuser 1 (401). It reports the XID frame to this latter. If Token RingUser 1 (410) accepts the connection, Token Ring DLC No 2 (412) sendsback an XID response to me remote station (430).

Afterwards, the remote station (430) sends a SABME to DLC No 2 (412) inresponse of which this latter responds with a UA response. Theconnection is now established between the remote station (430) and DLCNo 2 (412). From now on, data traffic can flow on this connection.

FIG. 7 describes the XID frame processing in a DLC whose Test responsehas been received first by the remote station. When an XID frame isreceived for an unavailable Token Ring user, DLC ignores the connection,but meanwhile, it adds a new entry in the Connection Cache Table andstores the station parameters.

The algorithm for the XID frame processing is as follows:

At step (700), an XID frame transmitted from a remote station isreceived by a Token Ring DLC. This latter checks in the destination SAPof the XID frame to determine if the Token Ring user associated to thisSAP is available at step (701).

If the Token Ring user is available, then the connection is establishedat step (702). Otherwise at stop (703), the connection cannot beestablished and the DLC searches for the remote station in theConnection Cache Table. At step (704), the DLC tests if the entry isfound in the Connection Cache Table.

If the remote station is already stored in the Connection Cache Table,DLC just ignores the XID frame at step (705). Otherwise, at step (706)since the remote station for which the connection is being refused isnot found in the Connection Cache Table, the DLC creates a new entry inthe Connection Cache Table and stores the remote station parameters.Note that this last entry overwrites the oldest entry in the CacheTable. In addition, the count parameter is set to 1, indicating that oneconnection has been refused for that remote station.

The index of the Connection Cache Table is incremented, and if itreaches the bottom of the table, it wraps to the top of the table.

And finally at step (707), the DLC ignores the XID frame.

FIG. 8 describes the Test frame processing according to the presentinvention.

When a Test frame is received in an all broadcast mode, all Token RingDLCs scan the Connection Cache Table to determine if a connection haspreviously been refused for the same remote station. Should the occasionarise in one of the Token Ring DLCs, it ignores the Test fame so as togive the opportunity for the remote station to obtain a backupconnection to the Token Ring user.

The algorithm for the TEST frame processing is as follows:

At step (800), each DLC receives a Test frame sent from a RemoteStation. Then, each DLC scans in the Connection Cache Table to determineif a connection has previously been refused for ma same remote stationat step (801). It checks in the Connection Cache Table at step (802) ifan entry of the remote station already exists.

At step (803), if the remote station is not found in the ConnectionCache Table, the DLC processes the Test frame command and sends a Testframe response back to the Remote Station. Otherwise, at step (804), theDLC increments its own counter in the Cache table, indicating that anadditional connection is being refused for that remote station.

Then, at step (805), the DLC checks if the counter has reached maximumvalue (N). If the maximum value (N) has not been reached, then the DLCignores Fe Test frame at step (806). Otherwise, at step (807), the DLCdeletes the corresponding entry in the Connection Cache Table. Thismeans that the next Test frame received from that remote station will beprocessed and responded by this DLC.

And finally at step (808), DLC ignores the Test frame and does notrespond.

FIG. 9 describes the content of the Connection Cache Table. TheConnection Cache Table (900) contains the Remote Station MAC address andthe Remote Station SAP. These parameters allows the DLC to identify theRemote Station. It also contains a connection Counter (count) indicatingthe number of unsuccessful connections of the remote station.

When a connection is refused for a remote station, a new entry (901)dedicated to this remote station is created in the Connection CacheTable. This new entry overwrite the oldest entry. Only a predeterminednumber M of the last unsuccessful connections are stored in theConnection Cache Table.

When a new entry is created, the Counter is set to 1. Then the index(903) is incremented and points toward the next entry (902). TheConnection Cache Table wraps automatically when the bottom of the tableis reached.

The connection cache table has a limited size (M entries). The number ofentries must be sufficient to contain all the possible connectionsbetween the remote stations and a Token Ring user during a certain time.The best rational is to have M equal to the maximum number ofconnections between all the different remote stations and a user.

However, this table should not be too large because it has to be scannedwhenever a Test frame is received, and a large table could impact on theperformances. The connection cache Table has an index, pointing to theoldest entry in this table, once all the entries have been filled. Sincethis table has M entries, the index points back to the first position atthe M+1 input. When a new connection is refused and the Source MACaddress/Source SAP is not yet in the cache table, these new parametersare added in the connection cache table at the entry pointed by theindex, and overwriting the oldest entry. The index is then incrementedand wraps when the end of the table is reached. In this way, a newconnection can be attempted to the destination user on the next Testframe received from said remote station.

In this document, in order to simplify the comprehension of theinvention, a configuration of two Token Ring DLCs (routes) and two TokenRing users is described. But this invention is applicable in a morecomplex configuration with I Token Ring Remote Stations (130,430)connected to K Token Ring DLCs (402,412) with their associated TokenRing Adapters (403,413) through J Token Rings (404,414,420) and L TokenRing users (400,410). This kind of configuration will not influence onthe different processes of the present invention.

Furthermore, it should be kept in mind that though the description isbased on the environment of Token Ring networks running multipleprotocols, it could be extended to other 802.2 DLCs such as bridgedFrame Relay or ATM LAN Emulation.

While the invention has been described in terms of preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

Having thus described our invention, what we claim is as follows:
 1. Amethod for load balancing a connection request in a communicationnetwork connecting a plurality of remote stations (130,430) to aplurality of destination users (400,410) through a plurality of networks(404,414,420) controlled by associated control means (402,412); saidmethod comprising the steps of: (a) transmitting (800) in an allbroadcast mode a Test frame from a remote station (430) to connectedcontrol means (402,412) among which only available control meansrespond; (a1) searching (801) respectively in a connection table (900)associated with each control means (402,412) an entry identifying saidremote station (430) so as to determine if a previous connection attempthas failed; (a2) ignoring (806,808) said test frame in said availablecontrol means (402,412) if a previous connection attempt has failed;otherwise, processing (803) a test response from said available controlmeans (402,412); and (a3) upon reception of test responses from saidavailable control means (402,412), transmitting (700) an XID frame fromsaid remote station (430) to an available control means that hasresponded first (b) On reception of an XID frame in said availablecontrol means (402,414) ignoring (705,707) said XID frame when itcontains an assigned destination user which is unavailable from saidcontrol means; and (c) when said assigned destination user is availablefrom said available control means, establishing a connection betweensaid remote station and said destination user.
 2. The method of claim 1further comprising the steps of: (b1) determining (701) from said XIDframe if said destination user is available for said available controlmeans (402,412); (b2) searching (703) for an entry in said associatedconnection table (900) for said remote station; and (b3) creating (706)a new entry for said remote station if it does by storing its parameterand setting its counter to 1 before ignoring (707) said XID frame. 3.The method of claim 2 wherein said step of creating (706) a new entryfor said remote station whose connection is refused, includesoverwriting new remote station parameters on an oldest entry so as toenable a connection attempt to the destination user on the next Testframe received from associated old remote station.
 4. The method ofclaim 2 further comprising the step of: incrementing (804) a counter insaid connection table (900) if an entry for said remote station existsand if said destination user (410) is still unavailable.
 5. The methodof claim 4 further comprising the steps of testing (805) the value ofthe counter in order to determine if it has reached a maximum value N;and deleting (807) the entry corresponding to said remote station (370)so as to enable a connection attempt to the destination user on the nextTest frame received from said remote station.
 6. A device for loadbalancing a connection request in a communication network connecting aplurality of remote stations (130,430) to a plurality of destinationusers (400,410) through a plurality of networks (404,414,420) controlledby associated control means (402,412); said device comprising: (a) means(800) for transmitting in an all broadcast mode a Test frame from aremote station (430) to connected control means (402,412) among whichonly available control means respond; (b) means (705,707) for ignoringreceived XID frames in said available control means (402,412) when theycontain an assigned destination user (410) which is unavailable fromsaid control means (402); said means (705,707) for ignoring said XIDframe further comprising a connection table (900), associated to eachcontrol means, having a plurality of entries, each entry beingassociated to a remote station and indicating if a previous connectionattempt by said remote station (430) through said control means to adestination user has failed; and (c) means (702) for establishing aconnection between said remote station (430) and said destination user(410) when said assigned destination user (410) is available from saidavailable control means (412).
 7. The device of claim 6 wherein eachentry of said connection table (900) comprises a counter whichdetermines the number of times said remote station (430) hasunsuccessfully attempted to connect to said destination user bytransmitting XID frames to said control means (402).
 8. The device ofclaim 7 wherein each counter has a maximum value N above which saidcorresponding entry is deleted so as to enable a connection attempt tothe destination user (410) on the next Test frame received from saidremote station (430).
 9. The device of claim 6 wherein said connectiontable is pointed by a rolling index having M entries so as to overwritenew remote station parameters on an oldest entry in order to enable aconnection attempt to the destination user on the next Test framereceived from associated old remote station.
 10. In a communicationsnetwork including a plurality of destination users, at least one remotestation, a plurality of networks interconnecting the plurality ofdestination users and the at least one remote station and networkinterface cards (NIC) coupling respective ones of the destination usersto respective ones of the plurality of networks, a method for loadbalancing a connection request including the steps of: (a) receiving insaid NICs a test frame with information seeking a route towards adestination user, from said at least one remote station; (b) uponreceiving an XID frame including identification information; (c)examining the XID frame; (d) it the XID frame contains an originaldestination user that is unavailable, said XID frame is ignored; and (e)if the XID frame contains an assigned destination user that is availablefrom at least one of NICs establishing a connection between said remotestation and said destination user.
 11. The method of claim 10 furtherincluding the step of searching entries in each connection tableassociated with each NIC to determine if a previous connection attemptby said station has failed; and if the previous connection attempt bysaid station has not failed issuing a response frame including routinginformation to the remote station.
 12. The method of claim 11 furtherincluding the step of terminating for this communication with said atleast one remote station for a predetermined time interval if theprevious connection attempt by said station has failed.
 13. A networkinterface card(NIC) for use in a communications network including: anadapter comprising a physical layer and including devices for couplingto the network and to the medium access control (MAC) layer functionscoacting operatively with a medium access controller to practice adesired network protocol; and a data link control (DLC) layer includingfunctions for routing frames, said DLC further including a memorystoring information identifying remote stations and frequency with whicha remote station is unable to connect with a selected resource in thenetwork; said medium access controller in response to a firstpredetermined frame searching the memory to determine if a stationidentified in the predetermined frame has been unable to connect withthe selected resource; and issuing a response frame only if the stationis not found in the memory.
 14. The NIC of claim 13 further includingthe controller not issuing a response frame if the station was found inthe memory.
 15. The NIC of claim 13 wherein the memory includes a tablehaving a section RMAC in which MAC addresses for stations are to berecorded, a section RSAP containing an indicia identifying a user and asection to record a count associated with each identifying entry in saidtable.
 16. The NIC of claim 15 further including the controller inresponse to a second predetermined frame, make an entry in the table bywriting a station MAC address in the second predetermined frame in theRMAC section of the table, the RSAP indication in the secondpredetermined frame in the RSAP section of the table and a logical “1”in the count section if this is the first entry for the station,otherwise increase the count by “1”.
 17. The NIC of claim 16 wherein thefirst predetermined frame includes an 802.2 test tame.
 18. The NIC ofclaim 16 wherein the second predetermined frame includes an 802.2 XIDFrame.
 19. The NIC of claim 13 wherein the desired protocol includestoken ring.